1. Technical Field
This invention relates to a digital beamforming receiver, such as global positioning system receiver, and more specifically to a system and method for precisely locating jamming signals from existing system data.
2. Description of the Prior Art
A global positioning system (GPS) receiver receives satellite signals transmitted from several of a set of GPS satellites, which are circling around the globe, and analyzes the received satellite signals to calculate the distance between each GPS satellite and the GPS receiver itself. Then, it calculates its current position from the calculated distances.
Where GPS systems are used in hostile environments, their reliance on data from multiple satellite sources makes them vulnerable to interference from a signal jammer. A signal jammer relies on the use of an active transmitter that overwhelms the receiver or feeds it false information. Such jamming signals can be the result of natural interference, or they can be artificially created with the intent of confusing the GPS system. Modern systems incorporate autonomous jammer nulling techniques, which allow the array antenna to be controlled by an autonomous system dedicated to the reduction of the jamming signal from a single jammer. These systems can decrease the influence of jammers on the system without excessively deforming the main or target detection beam.
While these autonomous systems work to neutralize the effects of the jamming signal, they do not precisely locate the jammer signal. Often, such information will be useful, as it facilitates the identification of the jamming source, allowing measures to be taken to neutralize the jamming. For example, in a military application it will be important to know where a jammer is located and whether it is hostile or inadvertent. Accordingly, a method for determining the location of a jammer source to a required degree of precision from data already provided by the autonomous jamming reduction systems would be desirable.
In accordance with one aspect of the present invention, a method is disclosed for locating signal jammers in a digital beamforming receiver having an antenna with a plurality of associated antenna orientations. An associated antenna gain value is calculated for a first of a sequence of the plurality of antenna orientations at each of a series of sample points. The antenna gain values from the first antenna orientation are evaluated for null spaces to obtain a set of candidate null locations. Associated antenna gain values are calculated and evaluated for subsequent antenna orientations only at the set of candidate null locations. Candidate null locations are eliminated from the set after any evaluation in which they are not found to be null spaces.
In accordance with another aspect of the invention, a computer program product is disclosed for locating signal jammers in a digital beamforming receiver having an antenna with a plurality of associated antenna orientations. An estimation routine calculates an associated antenna gain value for a first of a sequence of the plurality of antenna orientations at each of a series of sample points. A coarse search routine evaluates the antenna gain values from the first antenna orientation for null spaces to obtain a set of candidate null locations. The estimation routine and the coarse search routine calculate and evaluate associated antenna gain values for subsequent antenna orientations only at the set of candidate null locations. A candidate null location is eliminated from the set after any evaluation in which it is not found to be a null space.
In accordance with a further aspect of the invention, a method is disclosed for locating a jammer within a defined region. The region is first subdivided into smaller subregions. The subregion with the lowest antenna gain is selected by calculating antenna gain values at one or more representative points within the subregions. The region is replaced with the selected subregion, and the process is iteratively repeated until a termination event occurs.
In accordance with a further aspect of the invention, a computer program product is disclosed for locating a jammer within a defined region. A fine search routine iteratively performs a sequence of functions until the occurrence of a termination event. In each iteration, the region is subdivided into smaller subregions. The subregion with the lowest antenna gain is selected for an associated antenna by calculating antenna gain values at one or more representative points within the subregions. The region is then replaced with the selected subregion.
In accordance with yet another aspect of the invention, a system for locating signal jammers in a digital beamforming system having an antenna with a plurality of associated antenna orientations is disclosed. The system includes a central processing unit that calculates an associated antenna gain value for a first of a sequence of the plurality of antenna orientations at each of a series of sample points. The central processing unit then evaluates the antenna gain values from the first antenna orientation for null spaces to obtain a set of candidate null locations. The system further includes a working memory that stores the candidate null locations. The central processing unit calculates and evaluates an associated antenna gain for subsequent antenna orientations only at the set of candidate null locations. Candidate null locations are eliminated from the set after any evaluation in which they are not found to be a null space.